Regulators and contractors examine new techniques and hydraulically applied products.
By Carol Brzozowski
For years, erosion control has simply focused on methodologies that proved effective in containing erosion and establishing vegetation. Now, erosion control measures have ramped up to include an emphasis on going “green.”
There are projects that benefit from relatively temporary “soft” techniques (versus hard armor). They not only are favored for the manner in which they assist in controlling erosion and establishing vegetation but also are ecofriendly in that they don’t pose a danger to wildlife, interfere with mowers, or—in many cases—need to be removed when a project is over.
Many companies, such as North American Green in Evansville, IN, are seeing increased demand for biodegradable products. The company manufactures BioNet, a completely biodegradable erosion control blanket.
The company’s product line includes a single net straw blanket, a double net straw blanket, a double net straw-coconut blanket, and a double net coconut blanket. Product applications include bioengineering projects, wetland mitigation, riparian area protection, shaded areas, streambanks and shorelines, and other environmentally sensitive areas.
Lynne Finney of North American Green notes that the green building initiative has spurred interest in biodegradable products. “The two major categories we’ve really seen growth in are the TRMs [turf reinforcement mats] and the biodegradable products,” Finney points out. “TRMs, the green solutions, are more aesthetic, cost-effective, and easier to work with than rock or riprap.”
The pool of those interested in the biodegradable erosion control solutions has expanded from contractors, engineers, and transportation department managers to municipalities, public works directors, landscape contractors, and golf course administrators, says Finney.
The US Green Building Council has been a force in the growing interest in biodegradable erosion control solutions, Finney points out. At first, many within the industry viewed the organization as a “tree hugger” entity, but its initiatives have received widespread adaptation by communities throughout the United States, she adds.
North American Green last year received a Top Ten Green Building Award. “The environmental impact is here to stay,” says Finney. “Stormwater runoff and sediment are two of the biggest pollutants to our waters.” Until recently, she says, “People never really ‘got it’ that that’s what it was—it’s not just throwing trash in the streams.”
Comparing Costs, Evaluating Performance
Even though green building practices are starting to take hold throughout the United States, “green” erosion control techniques in some cases are taking longer to catch on.
“One of the reasons is cost,” says Joe Crea, national director of stormwater compliance with Richmond America Homes Corp. (MDC Holdings) in Denver, CO. “The more conventional approaches, such as wrapping a site in silt fence, are a lot less expensive upfront than if one were to incorporated an effective combination of erosion and sediment controls. But that doesn’t say you have to do your entire project in all conventional technology.
“Soil stabilization in general is often overlooked because of the upfront costs, and what is forgotten is that, in the long run, once the soil is stabilized, many dollars will be saved on more frequent maintenance of sediment controls”. Crea says under present economic conditions in the building industry, “We want to make sure we’re protecting our soils from erosion, but we also now need to be cost-cognitive.
“I enjoy this from a technical standpoint, but I am also looking after my company from a budget standpoint. When you have a municipality or state that allows for alternative types of practices that include both erosion and sediment controls, it allows more flexibility. But when you are limited to certain conventional BMPs [best management practices] and alternative BMPs are not accepted, you can’t really work on your budget, which is the case here in Colorado.”
Lew Manhart, an environmental monitor with the Virginia Department of Transportation (VDOT), tests new products as well as monitors environmental projects.
The VDOT has had the most experience with ENCAP’s PAM-12, and while the department has not conducted quantitative cost-effectiveness studies of the product, Manhart points out that the ability to make one pass with the product versus three with more traditional hydraulic applications results in time and labor cost savings.
John Parrish, a representative with CFP, a Ferguson Enterprise Co. in Raleigh, NC, notes that although some biodegradable erosion control is more expensive, he believes it’s worth the money.
“You get better germination and better initial plant growth with the natural netting than you do with plastic,” he says.
The cost of using biodegradable erosion control depends on the critical nature of the site, says Robert McGann, an estimator with Hydro-Plant Inc. in San Marcos, CA.
“The enforcement of the US Environmental Protection Agency in the San Diego region is probably one of the most strict on the West Coast. A lot is dictated by projects that are near waterways. In that case, they really want to button up their projects, and while the cost has some bearing, it’s more important things are stabilized in a very good way—that’s where the bonded fiber matrix will often be used,” he says.
“The benefits are long-range protection for no sediment-laden water leaving the project, which is a big issue,” he adds. “Another big benefit is it’s much more cost-effective than rolling out erosion control blankets.”
In addition to cost factors, convincing those who make decisions on what type of erosion control to use to try something different from what’s always been done is a challenge.
Crea knows of that firsthand. He has noted success with such products as Profile Products’ Flexterra—a flexible growth medium or mechanical bonded fiber matrix (MBFM) made of thermally refined wood fibers, crimped interlocking fibers, and additives—because it promotes good vegetation.
“My goal—other than helping Richmond with their stormwater program—is to get alternative technology like biodegradable hydraulic applications introduced and welcomed,” he says.
But hydraulically applied erosion control is not widely received throughout Colorado, where his company is based.
“Local municipalities think each category of the hydraulic application is the same. Tackifier mixed with seed—hydroseeding—is not the same as a bonded fiber matrix [BFM] or stabilized fiber matrix, which is cross-linked tackifiers and fibers. “We are currently testing [Profile’s] CocoFlex, made with coconut fibers,” he adds.
Among the government entities where hydraulically applied erosion control is being well received is Caltrans, California’s transportation department, where Crea, a former mid-Atlantic regulator and California consultant, had conducted training on hydraulic application of erosion control as a BMP.
Some Colorado towns are also testing hydraulic applications, such as Castle Rock.
“They follow Douglas County requirements, which say no hydraulic applications are allowed, but I have reviewed with them the proper design on our plans of where we would apply it. “Soil types, climatic conditions, and slope length and percentage are very important factors when considering hydraulic applications,” says Crea.
There are, of course, situations in which a hydraulic application is not applicable, he notes. “You would never put it in a channel or apply it in areas where the sheet flow will transition into what’s known as shallow concentrated flow, which initiates the rill-forming process, eventually leading to concentrated and channel flow conditions.”
“This is only applicable for sheet flow. We had to make sure wherever we were doing a pilot project that the slopes had the proper slope length and percentage requirements so the transformation from sheet flow to rill flow would not occur.”
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Photo: CFP |
| A gabion basket base and several tiers of 9-inch lifts using C-350 TRM, seeded soil mix, and green cuttings |
Weather is another consideration in using some biodegradable products and techniques, Crea says. “Hydraulic applications cannot be done during rain because of the required curing time,” though he notes some products such as Flexterra can be applied during light rainfall events.
One Flexterra application in Colorado that impressed some officials was its use by the Colorado Department of Transportation in remediating an area destroyed during the 2002 Hayman Fire 30 miles southwest of Denver, where 44,000 acres burned at high severity.
“It’s unbelievable how it is starting to become revegetated. The applied product is still lasting in the areas where they sprayed it,” says Crea.
Like hard armor, hydraulic applications are effective when properly conducted. Soil preparation is also important.
Knowing Your Site Conditions
Crea, who by background is a soil scientist, is currently working on a site project testing soil samples for textural and fertility properties.
“Whatever seed mix is required for a given municipality, we’ll have the proper fertility not just to get it to grow, but to thrive, so if we have to add any nutrients or soil amendments, we can do so during the soil preparation phrase,” he says.
Some people will assume a bad seed mix if it doesn’t germinate after a hydraulic application. A seed mix must have a “very high pure live seed rate” and the soil must be properly managed, Crea points out.
“Soil has horizons,” he says. “The top horizon is usually nutrient-rich. Everything below is nutrient-starved. During construction, the top horizon is not always preserved and the result is seed being put on soil that has little or no nutrients. Ultimately the vegetation is going to be sparse or won’t even take.”
A nutrient analysis yields information on what is needed to be added to increase fertility. Soil preparation should include surface roughening.
“You never want tough, compacted soil,” says Crea. “That’s what engineers call high bulk density. Think about that seed trying to penetrate it, the runoff that could generate from that slope, or the material that could even slide from it.
“By roughening up the soil in a proper fashion, you’re allowing that hydraulic application of the seed to settle in those grooves. The application will stick into the form. A roughened slope will have less friction than a hard-compacted slope.”
To show the comparison, Crea’s experiment will involve compacting one area of a slope, applying seed, and putting a blanket on it. Crea expects it to demonstrate that erosion control blankets don’t necessarily eliminate erosion.
“They break up the raindrop energy and reduce the amount of erosion underneath, but there still is erosion occurring. What I want to show is twofold: All that seed is going to end up at the bottom of the slope during the monitoring period because of how compact [the soil] is. Secondly, when we did a demo for Castle Rock last year, we showed quicker germination with Flexterra—and it thrived—compared with the 70/30 straw-coco blanket required now by all municipalities.” He plans to write about the study results in an attempt to guide regulators and other decision-makers through the process of different types of applications.
The design phase is the time to determine whether hydraulic applications are appropriate, Crea points out. “To put together an erosion/sediment control plan, first you need to look at the slopes on the project,” Crea says. “SWPPP [stormwater pollution prevention plan] consultants have plat plans that are blank sheets with no contours. Wouldn’t you want to be able to see where the lots are going to be and the contours, the topography? You can figure out if it’s even worth looking into the hydraulic avenue, given slope lengths and percentages, soil types, and climatic conditions.”
“The next step is to inspect the pre-project conditions—evaluate slope conditions, look at soils and current vegetation. You shouldn’t always be putting Kentucky bluegrass in a high desert area. You need to see what native plants are there, because that’s probably going to be required by the local municipality.”
Another key factor is determining how long slopes will sit, Crea says.
“Most regulations say if it’s going to sit inactive within 14 days, that slope has to get stabilized. Would it make sense to spend $0.03 a square foot on a fiber mulch or $0.10 a square foot on something like a Flexterra, when I only need it on that slope for three to four months because I’m going to come back in and put a retaining wall in?”
Another design issue is figuring out what’s going to happen in areas where there will be no homes, only landscaping.
“Are they going to need to be reworked down the road, have retaining walls? Are there going to be woody materials in there, or is it slated for grass? How long is it going to sit? Those answers allow me to choose the proper application,” says Crea. “Another handy tool during the design phase is the Natural Resources Conservation Service’s soil survey.”
Builders want to know about soil properties in order to determine if soils can be graded in the wintertime in the Northeast where they may easily clod during freezing and thawing conditions.
Questions to consider, says Crea: “Does the soil have good drainage properties? Does it support vegetation? Does it have limestone a foot beneath it? I mention limestone formations because you don’t want to put a sediment trap in that area. These factors help builders plan their construction activities and work around them as necessary.”
Demonstration Projects
Julian Richardson, owner of Delmarva Hydroseeding in Camden Wyoming, DE—a company that does commercial, landfill reclamation, and highway work—uses Earth Chem products on a daily basis in conjunction with hydromulch and BFM products.
“I’ve tried some others over the 15 years we’ve been in business,” he says. “Earth Chem, to me, is the best. It’s not cheap. We use it because it was approved by the Texas Transportation Institute. It has a good shelf life, and we swear by it.”
EarthBound is a soil stabilization polymer manufactured by Earth Chem in Fort Collins, CO. It’s formulated to stabilize soil structure and hold mulch in place. According to Texas Transportation Institute field studies, EarthBound supports prime vegetative growth and reduces soil erosion by 85% on 2:1 slopes. The product is said to increase water infiltration and retention as well as decrease soil crusting.
As seed and mulch stay in place, reseeding is unnecessary. EarthBound lasts four to 12 months in the soil.
When Richardson had met resistance in the county years ago, he offered to do a free demonstration with materials provided by suppliers. “They wanted to get the county soil conservation people to endorse bonded fiber versus matting for a large retention pond,” he says. “The savings to the customer is the labor intensity of putting down matting versus having a hydroseeding machine come out there and shoot three or four loads—to get the whole thing done and not have all that labor tied up in it.”
Richardson says his company is one of the few certified in Delaware to use the product. “We’ve helped to get the county to accept it,” he says. “They want everybody certified for using bonded fiber. We use it on all the highway work projects we do where they put topsoil down, so that the topsoil doesn’t erode down into the ditches with a heavy thunderstorm and then find its way to steams and ponds and out to the bay.
“The only time we wouldn’t use it would be in a flow line, and there we recommend using straw coconut blanket, depending on the severity of the water flow.”
Richardson says all his company uses is biodegradable products. “Some of our customers get sticker shock, but they just have to get over it, because all of the engineers design things that way,” he says.
California is open to hydraulically applied erosion control. There, Hydro-Plant Inc. in San Marcos performs hydroseeding and hydraulic soil stabilization for erosion control, using Super Tack from Rantec in Ranchester, WY, in a broad range of applications.
Basic hydraulic applications include simple forms of binders, says Estimator Robert McGann. The mid-range, such as Super Tack, is more effective because it addresses regional stormwater regulations. At the top of the pack is the bonded fiber matrix (BFM), which he says is most expensive.
Super Tack’s new formulation yields 80% of peak viscosity in five minutes after mixing and 90% by 15 minutes, while mixing easily without lumping. The tackifier system of fiber, adhesive, and soil bonds into a soil holding matrix to anchor mulch, seed, and fertilizer until vegetation takes root and prevents soil and sand erosion and fugitive dust. The product is 93% soluble and is made of nontoxic ingredients.
The benefits of its viscosity result in enhanced machine pump performance, creating a more uniform and controllable spray pattern; it keeps the tackifier in contact with the fiber during application, preventing drain-off at ground impact, and controls the rate at which the tackifier weeps off into the soil, maintaining fiber contact until curing can set up the final bond.
He says an advantage of BFMs is that they don’t pose a threat to the health of wildlife as the netting on some types of erosion control blankets can.
Some of the challenges in hydraulically applied erosion control products center on access, McGann points out. “Several years back, when we had a huge fire restoration project going on, we were called on to do a couple of isolated sites because some of the other contractors could not get to them with the equipment they had,” he says. “Access is one of the biggest issues there are, particularly when you’re trying to pump thicker, heavier slurries. We have specially designed pumps—the same pumps we use to pump Bermuda on golf courses.”
The State of Virginia also is open to hydraulically applied erosion control, and its department of transportation (VDOT) uses ENCAP’S PAM-12 extensively. The amendment was designed to reduce runoff and erosion, increase water penetration, and improve water efficiency.
Manhart’s department had conducted a trial two years ago at three different spots on a new road project in an effort to ascertain which new products on the market would offer the best erosion control and better ensuing vegetative growth.
The product was applied with a hydroseeding machine on cut slopes with large banks. They were steep slopes of 3:1 or 2:1. The cut slopes in the first test example were benched with terraces measuring 1.5 feet by 0.5 foot and served to catch sediment and dirt.
VDOT applied ENCAP PAM-12 hydraulically along with fertilizers, lime, and seed with favorable results. The department also applied a comparison sample with a traditional seed, mulch, and tackifier mix.
“When we looked at the end result, it was my assessment there was better growth and coverage of the vegetation on our PAM-12 slopes than on our regular straw slope,” says Manhart.
“We did the same thing on a fill slope. Basically, there was no observable difference in terms of the end result of erosion or sediment control or seed growth,” he says. “Where there is a big difference is in the total time spent hydroseeding and in preparing, seeding, and mulching the site.
“When you use the PAM-12, if you make one pass across, it doesn’t take much time. What we normally do is put the seed fertilizer and lime down and then come back, blow the straw, come back with a fiber mulch, and tack the straw so it doesn’t blow away.”
Manhart noted no statistical difference on the fill slope in seed germination and growth. On the cut slope, the grass that came up on the PAM-12 side was about a third taller than on the straw mulch side.
“We had similar coverage in both of those cases in terms of the amount of ground we covered with vegetation,” he says. “In an environment where straw is becoming more expensive, harder to get, and more costly to transport to the job site, we’re looking for other alternatives.
“Some of these alternatives offer some opportunities, like the polyacrylamides that bind soil particles together. Our observation is it helps to reduce erosion. It lessens raindrop impact, which means there’s less puddling on soil surface, so you also get less hardening over the soil. It allows the grass and other things planted to come up through it.”
There also are other benefits to biodegradable erosion control, notes Manhart. “We are looking at any kind of new product that will help us keep the dirt on the hillside and from running off the slope. We have a much better chance not only of getting vegetation established, because we are not washing our fines away. Secondly, if we keep it onsite, we’re certainly keeping it out of the Chesapeake Bay and out of our streams and rivers. In the end, that’s our whole objective.”
PAM-12 and PAM-12 Plus Turf Seed contains ENCAP’s Advanced Soil Technology, a formulation of water-soluble polymers called linear polyacrylamides. They are “watered out” of the granule when wet.
Through its soil-binding properties, the product increases water infiltration, opens soil porosity, increases seed emergence, reduces silt transport by surface water, and reduces rill erosion. Through its moisture management, PAM-12 reduces irrigation frequency, increases soil moisture retention, and promotes lateral movement of water through the soil structure.
One of its strengths is in use of forest fire restoration projects. “There are extreme slopes, with all vegetation removed. The soil is damaged due to high heat, which changes its properties to the worst,” explains Mike Krysiak, president of ENCAP in Green Bay, WI. “It creates hydrophobocity, which is the soil’s resistance to absorbing water. With 600 pounds per acre of PAM-12, you can effectively establish plant life, reduce erosion, and improve the hydrophobocity.”
Krysiak says another benefit of the technology is that “you can do so much with so little. Traditional mulches require 2,000 pounds per acre; PAM-12 takes 600 pounds per acre. That means fewer trips back to the water source. That’s an issue in many applications when water isn’t adjacent to the site.”
A Combination of Techniques
There are cases where soft and hard armor can be used in conjunction to address a particular challenge.
Such was the case in Raleigh, NC, where CFP helped address an erosion issue four years ago. The company supplies erosion control and soil stabilization materials and consults in the field during product installation. Among the many companies for which CFP is a distributor is North American Green.
Chavis Park is in downtown Raleigh, where two creeks converge. Sometimes when a thunderstorm blows through, the water level jumps a couple of feet in about 20 minutes and then goes down about as fast as it comes up, says Parrish. “It gives a whole new meaning to flash flood in this area.”The creek had been out of control, head-cutting and compromising a walk trail in the park, Parrish says. There had been some washouts in the creek that were undermining the trails that were up at the 12-foot level.
“In some of the bends in the creek where the water was washing, it was starting to eat the toe away and make the slope increase so it could compromise the trail at the top. You don’t want to have a sinkhole in the trail fall in all of a sudden,” Parrish says.
“To handle the flow at the base, we needed some hard armor as protection, so we put in gabions to act as armoring for the toe of the slope as well as for the creek channel,” he says.
The slopes had been 12 feet vertical in some areas. After the gabion layers were installed, they were 2:1 slopes.
Also at the site, CFP used North American Green’s C350 TRMs. “It has three layers of permanent netting but also has coconut fiber in it,” notes Parrish. “We would take soil and lift and wrap the face with C350. In between each lift, we’d lay live cuttings of natural materials such as willow sprigs so they would grow.
“Out of the heavy flow areas, we went in with a toe stabilization, built in a natural point, and put coir logs in to protect the toe of the slope surrounding the area. We covered the entire area with biodegradable C125 Double Net Coconut Blanket. It held through some pretty large storm events and vegetated nicely.”
Biodegradable erosion control products are quite effective in not only controlling erosion but establishing vegetation as well, says Parrish. “Natural products catch more sediment particles coming downstream in areas where it overflows. There also is more moisture retention for the plants to get a start, because the netting is natural and holds water. Plus, it will lie down and conform a little bit more with the soil line. Wherever you’re going to put [mat] down where it’s been seeded, it’s not flat, and the natural netting seems to conform more to the condition of the soil. Even though plastic is very soft and lays down flat, when [natural fiber] gets wet, it really sticks to the contour.”
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Photo: Virginia DOT |
| Hydroseeding PAM-12 along with lime, fertilizer, and seed onto grooved cut slope |
After the Fire
Post-fire remediation is an area where biodegradable erosion control is taking off.
Mike Perry, chief executive officer of Forest Concepts in Auburn, WA, says that since his company began manufacturing WoodStraw in June 2006, more than 1,600 tons have been used in 20 national forests and three Bureau of Land Management districts for wildfire rehabilitation, mine reclamation, and road maintenance or road removal. It has also been used in areas to protect the habitat of a threatened and endangered cutthroat trout.
WoodStraw is a biodegradable wood-strand erosion control mulch that is weed-free, has high wind resistance, can last in excess of two years, and is stable on steep slopes.
One of its recent uses occurred in Oregon. Fires in Foster Gulch and McLain Creek started on July 23, 2006, as a result of lightning. They burned together later in the week and became known as the Foster Gulch Complex.
Before the fire was contained on August 9, it encompassed a total of 53,547 acres, including 31,695 acres belonging to the Bureau of Land Management, 18,871 acres of private land, and 2,973 acres belonging to the US Forest Service.
Mike Woods, the natural resource manager for the Vale District Bureau of Land Management in Baker City, OR, says the fire was the largest in Lake County for at least 75 years. “The intensity was quite high and severe. We had some real concerns for erosion issues, come spring runoff,” he says.
The fires had left white ash 3 feet deep. “One of our concerns was the erosion, plus noxious weed issues,” he says.
Aerial straw mulching was used in the most severely burned areas. One job encompassed 400 acres of straw mulch at 1 ton per acre, 200 acres of straw mulch at 1.5 tons per acre, and 77 acres of WoodStraw at 3.5 tons per acre. In total, 690 acres were aerially seeded.
In another project, 100 acres were aerially straw mulched at 1.5 tons per acre with 600 acres aerially seeded. Some 2,710 acres at a lower elevation were aerially seeded, while 210 acres northeast of Richland were drill-seeded. Additional work was done in the late summer and fall of 2006.
“We knew we wanted to put some mulch down,” says Woods. “The green straw has its place when wind isn’t a factor. The WoodStraw and green straw were both dropped by air from a helicopter, because of the steepness of the slope.
“Once we got things sorted out, Forest Concepts worked with us in not baling the bales so tightly so they would open up and scatter a little better after it was dropped from the air,” Woods says. “By and large, we were really pleased with it. We were fortunate enough not to have much of a snow pack this year, and we haven’t had any really serious rain events to test it, so that helped us out when we were dealing with fairly steep slopes. Our site is recovering and the seed is establishing at this point.”
Woods says he hasn’t used any of the smaller bales of WoodStraw for hand placement, although that’s starting to catch on in the West.
But he still favors it “because you can place it precisely, get a fair distribution, and get it as thick as you want it for aerial treatment. For straw bombing from the air, it takes a pilot with some experience with the material because basically you are opening the cargo net 700 feet above the ground. It depends on the velocity and approach to the smoke to determine how well it is spread.
“We realized we have some missed slopes on the hillside,” he notes, “but it did spread surprisingly well considering the size of the bales. And you want to keep those bales as dry as you can, so they don’t have any moisture.”
Woods says a major benefit of WoodStraw over green straw is that while green straw is less expensive, he can be sure with WoodStraw that there is little or no risk of introducing noxious weeds.
“The WoodStraw is a clean product, and that has a lot of value in it as well,” he says. “We’re confident that the green straw used last winter was certified weed-free, but with that much volume, there’s always a chance that one of those bales did establish.”
Woods says he foresees WoodStraw being used more by not only the Bureau of Land Management but also other agencies in the western US for mulching for emergency stabilization after fires.
Wildlife Safety
Other options abound.
Conwed Global Netting in Minneapolis, MN, makes biodegradable polymers and a wildlife-friendly erosion control blanket, NatureZone netting.
“You’d use these products under two distinctly different conditions,” says Brad Budde of Conwed. “In the case of the NatureZone netting, it would be used when concerns for environment safety—typically animals—were important. We’ve shown that NatureZone-shaped netting is effective in not trapping snakes, compared to how square netting has in the past.
“The difference between NatureZone netting and traditional netting is the shape of the aperture; that shape allows animals to freely pass through because the expansion of that aperture is larger as a percentage of its static shape than of the expanded shape.”
Additionally, Conwed offers biodegradable and degradable polymers.
Carol Brzozowski is a journalist in Coral Springs, FL.
EC - November/December 2007
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